Broken link to coverage build results

[Richard Wall]

The link to coverage results redirects to localhost:8080

 * https://buildbot.twistedmatrix.com/builders/twisted-coverage.py/builds/1272

eg
 * https://buildbot.twistedmatrix.com/builds/twisted-coverage.py/twisted-coverage.py-r38135 >>
 * http://localhost:8080/builds/twisted-coverage.py/twisted-coverage.py-r38135/

The problem seems to be a missing slash eg
 * https://buildbot.twistedmatrix.com/builds/twisted-coverage.py/twisted-coverage.py-r38135/